The present invention relates to a locking device for seat belts intended for vehicles, of the type in which a strap forming a part of the seat belt is automatically drawn into a casing and wound up on a rotatable coiling shaft when the belt is not used, to temporarily lock the shaft.
Is is previously known to arrange locking of the shaft in a coiling device by providing the shaft with a body rotating with the shaft, in said body there being arranged a number of displaceable locking bodies arranged to be moved to a locking position in which they engage with a fixed toothed ring outside the rotational path of the rotating body, so that the shaft is prevented from rotating and withdrawal of the strap of the seat belt cannot take place, whereby the person wearing the seat belt is safely kept in place. Displacement of the locking bodies to the locking position can thereby take place either in response to a rapid withdrawal of strap, the locking device thus being responsive to strap movement, or in response to an acceleration or retardation of the vehicle, the locking device thus being responsive to vehicle movement. The locking device can also be made so that it is responsive to both strap and vehicle movement.
By having the locking bodies in the known locking catch devices arranged in a body rotating with the shaft, the locking bodies will be brought into contact with the fixed toothed ring at a large velocity relative to it, which can result in bouncing and unreliable locking function. By reason of the displaceability of the locking bodies in the body rotating with the shaft, there also easily arises a rattling sound in the locking catch device caused by movements or vibrations of the locking bodies even for slow withdrawal of strap from the coiling device.